The present invention relates to cooling systems and in particular to cooling systems for internal combustion engines, in which a fan is driven by the engine.
It is known to provide engine cooling fans driven by the engine through a viscous coupling. The viscous coupling permits the cooling fan to free-wheel while the coolant temperature is below a predetermined value, the coupling engaging when the temperature of the coolant rises above that value. When the coupling is engaged the fan is however driven at engine speed or some proportion of engine speed.
With electrical cooling fans, it is possible to control the speed of the fan totally independently of engine speed. However, electrical fans have a significant power requirement and consequently a means of power generation driven by the engine must be provided to generate sufficient energy when required. As the generation means is driven continuously it will impose a load on the engine whether the electrical fan is driven or not.
The present invention provides an engine driven cooling fan which may be driven independently of the speed of the engine, the fan when not being driven imposing little or no load on the engine.